Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$95.98	13.617%	$109.0496	$109.05	$109.05	$109.00
Purchase #2	$245.29	12.421%	$275.7575	$275.76	$275.75	$275.80
Purchase #3	$56.86	13.693%	$64.6458	$64.65	$64.65	$64.60
Purchase #4	$55.85	6.202%	$59.3138	$59.31	$59.30	$59.30
Purchase #5	$40.61	12.546%	$45.7049	$45.70	$45.70	$45.70
Purchase #6	$65.59	9.790%	$72.0113	$72.01	$72.00	$72.00
Purchase #7	$224.37	12.729%	$252.9301	$252.93	$252.95	$252.90
7 purchase totals =	$784.55		$879.4130	$879.41	$879.40	$879.30